Allow comments to be cooked from TASTy

[abgruszecki]

In the doctool, we need to implement resolve Scaladoc comment variables (@define) - see https://docs.scala-lang.org/overviews/scaladoc/for-library-authors.html#macros for the only documentation I'm aware of.

Dottydoc resolved those under YcookComments flag, but the result of that was not serialised to TASTy. We anyway came to the conclusion that for design reasons, we want to avoid adding expanded comments to TASTy.

This means that we need to investigate whether the code responsible for "cooking" comments could also be ran when classes are loaded from TASTy.

[abgruszecki]

@bishabosha I gave the problem some thought and I believe the best time to get started on this would be after #10143 is fixed, since stdlib is the best test case for this issue.

[bishabosha]

@abgruszecki ok thanks, I'll take a look at that point

[abgruszecki]

Done.